What is Sedimentation?
Sedimentation is physical operation and separates solid particles with a density
higher than that of the surrounding liquid. In a tank in which the water flow
velocity is very low, the particles tend to go to the bottom under the influence of
gravity. As a result, the supernatant liquid becomes clarified, while the particles
at the bottom form a sludge layer, and are then subsequently removed with the
sludge. Sedimentation is a unit operation of high importance in wastewater
Main applications of sedimentation in wastewater treatment are:
1. Preliminary treatment.
Grit removal (sedimentation of inorganic particles of large dimensions)
By Grit chamber
2. Primary treatment.
Primary sedimentation (sedimentation of suspended solids from the raw sewage)
By Conventional primary clarifiers, with frequent sludge removal or
By Septic tanks
3. Secondary treatment.
Secondary sedimentation (removal of mainly biological solids)
By Final sedimentation tanks in activated sludge systems
By Final sedimentation tanks in trickling filter systems
By Sedimentation compartments in anaerobic sludge blanket reactors
By Sedimentation ponds, after complete-mix aerated lagoons